Nanocellulose is used to prepare lithium-sulfur flexible batteries

Lithium-sulfur batteries have attracted much attention because of their high theoretical volume energy density (2800 Wh L-1) and gravity energy density (2500 Wh kg-1) and their capacity far exceeds that of traditional lithium-ion batteries. Therefore, the development of high-performance flexible lithium-sulfur batteries can better meet the needs of future flexible wearable electronic devices. In addition, elemental sulfur has outstanding characteristics such as abundant resources and low price, making lithium sulfur batteries an attractive EES. First, during the electrochemical cycle, the volume change of sulfur particles will lead to structural changes of the active material, thereby reducing capacity. Secondly, insulating sulfur and Li2S will slow down the electrochemical kinetics. Third, polysulfides are easily dissolved in the electrolyte, resulting in 'shuttle phenomenon'. To solve these problems, various attempts have been made in the design and preparation of new electrodes, electrolytes and separators.

1. Flexible electrode

Nanocellulose and active materials can be integrated together to make composite electrodes of LSB. Due to its abundant hydroxyl groups, entanglement networks and high aspect ratios, flexible CNF has been developed as a component for the manufacture of independent, sandwiched structures, long-life LSB cathode materials with high area mass loads. Interconnected CNF/CNT layers were prepared on both sides of the active layer to provide efficient electron transport and capture of polysulfides. The physical encapsulation and chemical functionalization (especial N-doping) of carbonaceous materials (graphene and CNT/CNF fibers) have a synergistic effect on the chemoadsorption of lithium polysulfide, thus achieving good electron conductivity and suppressing the Dissolution and migration of sulfides. With the average load of sulfur of 8.1 mg cm-2, the electrode has a high capacity of ≈8 mAh cm-2 and the average Coulomb efficiency is ≈97.3%. Wu et al. reported high-performance lithium polysulfide batteries with local concentration-derived heterogeneous Li2S2/Li2S deposition on biphasic MWCNT/CNF/NiCo2S4 self-standing paper. High-performance independent soluble lithium polysulfide (LiPS) host-MWCNT/CNF/NiCo2S4 (3.5 mg/cm-2) catalyzes 2.85 mg/cm-2 (sulfur-based)-loaded LiPS.

2. Flexible electrolyte/diaphragm

A nanoscale microfibrous cellulose polymer system was prepared as the electrolyte for lithium-S rechargeable batteries. The polymer electrolyte has excellent thermal stability, high ionic conductivity and a stable interface with lithium metal. Batteries with abundant natural cellulose-based polymer electrolytes as separators show higher specific capacity, excellent Coulomb efficiency, better cycle stability and rate capabilities under ambient conditions. Hydrophilic, environmentally friendly, low-cost CNCs are proposed for high-performance LSBs as multifunctional polysulfide barrier layers. Functional theory. In addition, the CNC can also act as a polysulfide barrier on the separator, preventing the polysulfide from passing through to the lithium anode. Therefore, the prepared LSB can exhibit excellent cycling performance even under conditions of up to 90 wt% sulfur content (63 wt% sulfur content in the cathode), loads up to 8.5 mg cm-2 and temperatures up to 60 °C. .

In summary, nanocellulose- based hybrid materials are expected to be used as electrodes, electrolytes and separators for high-performance LSBs. However, there are still challenges such as how to achieve a high active material load in the cathode while maintaining the high mechanical strength, flexibility and excellent electronic conductivity of the nanocellulose-based composite. How to alleviate polysulfide shuttle and maintain stable and long-lasting effects remains a challenge for Therefore, rational design and optimization of the stratified porous structure and surface/interface characteristics of nanocellulose are crucial for the construction of high-performance LSBs.nanocellulose- based electrodes and separators.